1. Technical Field
The present invention relates to an antenna device suited to be mounted in a small-sized terminal unit such as a cellular phone.
2. Related Art
A chip antenna has received much attention that is typically constituted by a rectangular-parallelopiped dielectric chip and a flat-plate-shaped or meander-shaped planar antenna embedded therein. As shown by way of example in FIG. 2, a chip antenna of this kind is mounted on a printed circuit board 1 with which the chip antenna is received inside an exterior casing 2 of the terminal unit.
In FIG. 2, reference numeral 3 denotes an antenna conductor; 4, a dielectric chip into which the antenna conductor 3 is embedded; 5a, a lead terminal led out from an end face of the antenna conductor 3 to the outside; and 5b, a fixture terminal. The chip antenna is mounted on the printed circuit board 1 by soldering the lead and fixture terminals 5a, 5b to prescribed portions of the printed circuit board.
Unlike a conventional rod antenna, the aforementioned antenna device or chip antenna has no projections projecting outwardly from the exterior casing. Thus, the antenna device is free from a bending failure and can improve the external appearance of the exterior casing, i.e., the terminal unit.
Since the chip antenna must be received in a limited space inside the exterior casing, outer dimensions of the chip antenna, in particular, its vertical position in the casing is considerably restricted. Specifically, the antenna conductor 3 is positioned at a limited or low vertical position relative to a grounding conductor (not shown) formed in the printed circuit board 1, making it difficult to heighten the vertical position for further improvement in antenna performance.
To improve the antenna performance, an attempt may be made to embed the antenna conductor 3 into the exterior casing 2 as shown in FIG. 3 so as to place the antenna conductor 3 at a higher vertical position relative to the grounding conductor (GND surface) of the printed circuit board 1. However, to embed the antenna conductor 3 in the exterior casing 2 made of plastic, which is generally fabricated by injection molding, a support mechanism must be provided in a molding die to support the antenna conductor 3 therein, requiring a complicated die structure. In addition, the fabrication process of the exterior casing 2 into which the antenna conductor 3 is embedded is also complicated, so that the finishing accuracy and hence the external appearance of the exterior casing may be degraded.
An object of the present invention is to provide an antenna device having an improved antenna performance and capable of being accommodated in a small-sized terminal unit such as a cellular phone, without degrading the external appearance of the terminal unit.
According to the present invention, an antenna device is provided, which comprises a dielectric chip adapted to be fitted in an aperture formed in an exterior casing of a terminal unit such as a cellular phone, the dielectric chip having an outer surface thereof cooperating with an outer surface of the exterior casing to form part of an outer surface of the terminal unit, and an antenna conductor embedded into the dielectric chip and extending along the outer surface of the dielectric chip.
With this invention, the dielectric chip of the antenna device is so disposed as to form part of the outer surface of a terminal unit, thereby permitting the antenna device to be accommodated inside the terminal unit without causing a degraded external appearance of the terminal unit, and the antenna conductor is embedded into the dielectric chip so as to extend along the outer surface of the dielectric chip, whereby the antenna conductor is placed sufficiently away from a grounding conductor of the terminal unit, to improve the antenna performance of the antenna device.
In the present invention, preferably, the antenna device is accommodated in the terminal unit having a printed circuit board that is disposed inside the exterior casing away from the aperture in the height direction of the exterior casing. Preferably, the antenna conductor embedded into the dielectric chip extends substantially in parallel to the outer surface of the dielectric chip, whereby the antenna conductor is placed at a vertical position sufficiently far from a grounding conductor that is formed, e.g., on the printed circuit board, to improve the antenna performance.
Preferably, the dielectric chip is provided with a fixture for fixing the dielectric chip to the printed circuit board. Alternatively, the dielectric chip is provided with a fixture for fixing the dielectric chip to the exterior casing. By fixing the dielectric chip of the antenna device, the antenna device is prevented from being unintentionally pushed further into the terminal unit to thereby prevent damages to the antenna device and components mounted on the printed circuit board.